Ms Powell told Sky News this morning that her words had been "misrepresented" and "blown out of all proportion". She reportedly contacted the police herself after being advised to by the television producers who interviewed her.

Winnie Johnson, mother of Keith Bennett Credit: Dave Thompson/PA Wire

Keith Bennett is the only one of Brady's victims who body has not been found. He was snatched on June 16 1964 after he left home to visit his grandmother

Winnie Johnson, his mother, is not aware of the recent developments. Over the years, she has appealed directly to Brady for him to reveal the final resting place of her son.

Ms Johnson's lawyer, John Ainley, said that members of Ms Johnson's family are "sceptical" about the news and that they consider it to be in her best interests to remain unaware of the claim until it is substantiated. Ms Johnson is very ill with cancer and lives in a hospice.

Mr Ainley added that it was "very timely" that the news had emerged just a day before the documentary is due to be aired.

The director of the documentary, Paddy Wivell, told the BBC that the claim should be treated with caution. He said: "This seems to me like very much part of Brady's pathology, one of power and control.

"He is a sadistic psychopath and it would appear that this is some sort of victory dance, a kind of power game."

Brady and his partner, Myra Hindley, were responsible for the murders of five youngsters in the 1960s. They lured children and teenagers to their deaths, with victims sexually tortured before being buried on Saddleworth Moor above Manchester.

Brady was sentenced to life at Chester Assizes in 1966 for the murders of three of the children.

Hindley was convicted of killing two of them and for shielding Brady. She too was jailed for life.

In 1987, the pair finally admitted killing Keith and Pauline whose murders had remained officially unsolved.

Hindley died in jail in November 2002, aged 60. Brady has spent the last 25 years at the high-security Ashworth Hospital in Merseyside.